Depends on the ammo. The 100 mm Hohlladungsgranate (HEAT) was able to penetrate 390 mm steel, which is enough to kill Leo 1 and M-60 with one shot. The Unterkaliberpfeilgeschoss (sub caliber darts, APFSsomething in NATO slang) penetrated 310 mm at 1.000 meters distance and 290 mm at 2.000 m. It had not had a problem to destroy a Leo 1 and M-60. With the T-55AM (soviet designation), T-55AM2B (east german designation) the missile Bastion was part of the ammo. Up to a maximum combat range of 4.000 meters this missile could kill all tanks of the late 1980, when used in top attacker mode. Useless against tanks were the Panzergranate (AP) and Splittersprenggranate (HE).
The HESH, HEAT and APFSDS ammo of L-7 gun of Leo-1 and M-60 (okay, the americans called the L-7 M68, but it was mostly the same gun) were able to kill a T-55 at a range of 2.000 meters. But they were not able to penetrate the frontal armour of the T-55AM (T-55AM2B).
The chance to survive of a T-72 depends a lot of the version. It had changed through the years dramatically. There were T-72 version which a Leo 1 could kill at 2.000 meters, while other T-72 versions were nearly unvulnerable in a duell situation at 500 meters distance.
Here some examples how the frontal armour of the T-72 changed through the years: